/*******************************************************************************
 * Copyright (c) 2000, 2004 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 * 
 * Contributors:
 *     IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.core.runtime;

/**
 * The <code>IProgressMonitor</code> interface is implemented
 * by objects that monitor the progress of an activity; the methods
 * in this interface are invoked by code that performs the activity.
 * <p>
 * All activity is broken down into a linear sequence of tasks against
 * which progress is reported. When a task begins, a <code>beginTask(String, int)
 * </code> notification is reported, followed by any number and mixture of 
 * progress reports (<code>worked()</code>) and subtask notifications 
 * (<code>subTask(String)</code>).  When the task is eventually completed, a 
 * <code>done()</code> notification is reported.  After the <code>done()</code>
 * notification, the progress monitor cannot be reused;  i.e., <code>
 * beginTask(String, int)</code> cannot be called again after the call to 
 * <code>done()</code>.
 * </p>
 * <p>
 * A request to cancel an operation can be signaled using the 
 * <code>setCanceled</code> method.  Operations taking a progress
 * monitor are expected to poll the monitor (using <code>isCanceled</code>)
 * periodically and abort at their earliest convenience.  Operation can however 
 * choose to ignore cancelation requests.
 * </p>
 * <p>
 * Since notification is synchronous with the activity itself, the listener should 
 * provide a fast and robust implementation. If the handling of notifications would 
 * involve blocking operations, or operations which might throw uncaught exceptions, 
 * the notifications should be queued, and the actual processing deferred (or perhaps
 * delegated to a separate thread).
 * </p>
 * <p>
 * Clients may implement this interface.
 * </p>
 */
public interface IProgressMonitor {

    /** Constant indicating an unknown amount of work.
     */
    public final static int UNKNOWN = -1;

    /**
     * Notifies that the main task is beginning.  This must only be called once
     * on a given progress monitor instance.
     * 
     * @param name the name (or description) of the main task
     * @param totalWork the total number of work units into which
     *  the main task is been subdivided. If the value is <code>UNKNOWN</code> 
     *  the implemenation is free to indicate progress in a way which 
     *  doesn't require the total number of work units in advance.
     */
    public void beginTask(String name, int totalWork);

    /**
     * Notifies that the work is done; that is, either the main task is completed 
     * or the user canceled it. This method may be called more than once 
     * (implementations should be prepared to handle this case).
     */
    public void done();

    /**
     * Internal method to handle scaling correctly. This method
     * must not be called by a client. Clients should 
     * always use the method </code>worked(int)</code>.
     * 
     * @param work the amound of work done
     */
    public void internalWorked(double work);

    /**
     * Returns whether cancelation of current operation has been requested.
     * Long-running operations should poll to see if cancelation
     * has been requested.
     *
     * @return <code>true</code> if cancellation has been requested,
     *    and <code>false</code> otherwise
     * @see #setCanceled(boolean)
     */
    public boolean isCanceled();

    /**
     * Sets the cancel state to the given value.
     * 
     * @param value <code>true</code> indicates that cancelation has
     *     been requested (but not necessarily acknowledged);
     *     <code>false</code> clears this flag
     * @see #isCanceled()
     */
    public void setCanceled(boolean value);

    /**
     * Sets the task name to the given value. This method is used to 
     * restore the task label after a nested operation was executed. 
     * Normally there is no need for clients to call this method.
     *
     * @param name the name (or description) of the main task
     * @see #beginTask(java.lang.String, int)
     */
    public void setTaskName(String name);

    /**
     * Notifies that a subtask of the main task is beginning.
     * Subtasks are optional; the main task might not have subtasks.
     *
     * @param name the name (or description) of the subtask
     */
    public void subTask(String name);

    /**
     * Notifies that a given number of work unit of the main task
     * has been completed. Note that this amount represents an
     * installment, as opposed to a cumulative amount of work done
     * to date.
     *
     * @param work the number of work units just completed
     */
    public void worked(int work);
}
